This invention relates to a transistor amplifier and, more particularly, to a transistor amplifier comprised of cascaded stages each formed of a plurality of field effect transistors having triode-type dynamic characteristics.
The use of a field effect transistor (FET) having triode-type dynamic characteristics offers many advantages which cannot be obtained from conventional FET's which have pentode-type dynamic characteristics. For example, harmonic distortion is reduced and switching characteristics are improved for the FET having triode-type dynamic characteristics. Also, this type of FET has a greatly improved linearity function. Consequently, the FET having triode-type dynamic characteristics finds ready application in high fidelity audio equipment, especially as the output stage of a power amplifier.
Because of the advantages obtained from such an FET, it is desirable to use this device in various stages of an audio amplifier to provide non-distorted amplification of small signals. However, FET's having triode-type dynamic characteristics admit of considerably smaller amplification factors than conventional field effect transistors. Thus, in order to attain the requisite large voltage gain for a practical small signal amplifier, it is necessary to connect a plurality of this type of FET in cascade. Unfortunately, although the desired voltage gain can be attained, the cascading of many FET stages results in a deteriorated signal-to-noise ratio. It is, therefore, desired to construct a small-signal amplifier which is capable of producing efficient voltage gain, but not at the cost of poor signal-to-noise.